This invention relates in general to vehicle ignition systems and, in particular, to ignition systems for vehicles having an air heater element for heating pre-start combustion air prior to starting the vehicle engine and having a vehicle battery powered auxiliary or emergency steering system which is actuated upon engine failure during operation of the vehicle.
More specifically, but without restriction to the particular use which is shown or described, this invention relates to a vehicle ignition circuit which automatically electrically isolates an auxiliary steering system from the vehicle battery upon energization of an air heater element for heating pre-start combustion air prior to engine starting to thereby eliminate unnecessary power drain on the vehicle battery.
In the operation of large vehicles such as those utilized in the construction machinery industry, due to the size of the vehicles and the functions they perform hydraulics are utilized to control steering and braking of the vehicle as well as the functions of various auxiliary equipment. While power steering and brake systems are required on such vehicles due to the vehicle size and weight, they can present a safety hazard in the event of engine failure or failure of the engine drive hydraulic pump such as occurs when the engine stalls or fails during vehicle operation. Therefore, it is necessary to have an auxiliary or emergency hydraulic pump to supply pressurized hydraulic fluid to control vehicle braking and steering in order to safeguard the machine operator and others who may be in the area where the vehicle is operating.
The pressurized hydraulic fluid required for power steering and power braking is normally provided by an engine driven hydraulic pump which supplies the power steering and brake units, as well as operating the hydraulically powered auxiliary equipment utilized with the vehicle. However, when the vehicle engine stalls or stops during operation, the hydraulic pump supplying fluid to these components is no longer driven by the engine and, therefore, hydraulic fluid pressure is lost which results in the loss of power steering and brakes.
In order to eliminate this potential safety hazard, auxiliary or emergency hydraulic pumping systems are incorporated in such vehicles. Various auxiliary or emergency hydraulic pumping systems are disclosed in the prior art and such prior art systems generally are activated by the closing of a sensor valve in the hydraulic system. The sensor valves have electrical contacts which are held open by the flow or pressure of the hydraulic fluid during engine operation to electrically isolate the auxiliary or emergency system. When the vehicle engine stalls or a failure in the hydraulic system occurs, the sensor valve closes to electrically couple the auxiliary system to the vehicle battery. While such systems provide a safeguard to prevent accidents, the closure of the sensor valve due to the absence of hydraulic fluid pressure or flow creates an unnecessary drain on the vehicle battery by not automatically electrically isolating the auxiliary system during engine start-up when the auxiliary system is not needed and maximum electrical power is required.
One system overcoming this problem and utilizing an electrically driven motor and pump powered by the vehicle battery to provide high-pressure hydraulic fluid to the vehicle brake and steering system in the event the vehicle engine or the engine-driven hydraulic pump fails or is inoperative is disclosed in co-pending application Ser. No. 751,378, filed Dec. 17, 1976, now U.S. Pat. No. 4,079,806, under the title "VEHICLE STARTING CIRCUIT TO BY-PASS AUXILIARY STEERING SYSTEMS", of which I am a co-inventor. In the system disclosed in this co-pending application, the electric motor driven hydraulic pump is automatically energized to provide pressurized hydraulic fluid to the steering and brake mechanism upon the occurrence of an emergency condition such as the failure of the engine during operation. The system disclosed and claimed therein automatically electrically isolates the vehicle battery powered hydraulic pump when starting the vehicle in order to eliminate an unnecessary drain on the vehicle battery.
As is well known to those in the construction machinery or earthmoving equipment field, it is sometimes desirable or necessary to heat the intake air used for the vehicle engine prior to attempting to start the vehicle. Since such heating occurs prior to attempting to start the vehicle engine, it is not necessary that the auxiliary or emergency hydraulic pump unit be energized when the intake air is being heated by the air heater element. Therefore, it is desirable that the vehicle battery powered electrical motor and pump unit also be automatically electrically isolated during heating of the pre-start combustion air to prevent another unnecessary power drain on the vehicle batteries. Since there is no hydraulic fluid pressure or flow in the hydraulic system at this time, the sensors for the auxiliary or emergency hydraulic system will be closed and the auxiliary system will be coupled into the vehicle ignition circuit unnecessarily draining the vehicle battery.
In order to eliminate imposing this unnecessary drain on the vehicle battery when the intake air is being heated, it is desirable to isolate the electrically driven motor and pump unit from the vehicle battery not only during engine startup, but during heating of the pre-start intake air.